docs: def condition_indices(df):
      '''
      Returns a pandas Series with condition indices of the df columns.
  
      Args:
          df: pandas DataFrame with columns to run diagnostics on
      '''
      eigvals = eigenvalues(df)
      cond_idx = np.sqrt(eigvals.max() / eigvals)
      return pd.Series(cond_idx, df.columns, name='Condition index')